Vacuum pump



M. E. JOHNSON VACUUM PUMP Filed Jan. 2. 1951 May 19, 1953 m w 0 J a .u m m u IN V Eh TOR.

A T TOR/V5 Y5 Patented May 19, 1953 umreo STATES PATENT? oFFicE VACUUM PUMP Application J anuary: 2, 195-13. Seriall-Na203;94&

3 Claims. 1;

This invention relates to vacuum. pumpsandis: particularly concerned, with vertical diffusion pumps-of theiractionating type One type of. pump commonly-employed for pro.- ducing, high vacuum .is the vertical concentric diffusion pump. Thi pump. is characterized by. having a.generallycylindricalvertical pump cas-- ingiwith. aplurality of concentric vapor chimneys. disposed: inthe. casing and generally concentric withthecasing. The vapor chimneys .are. rigidly. secured to. each other and-have theirlower. ends extending to the: bottom. of the pump. casing to. form a plurality of. concentric boiler compart.- ments,. andthe vapor chimneys terminate) upwardly. in vjet nozzles-from: which pumping vapors emerge. to exert.theirpumpingaction in. the pumpcasing. The boiler compartments are intercon-. nected in series by an aperture inzthe lower end of each chimney whereby pump fluid. flows through-,the. compartments. in turn andis frac:-- tionated so thattthe'. lowest vaporv pressure com-- ponents-exertttheir. pumping actionfrom the. jet nozzlenearest: the-ahigh, vacuum inlet. and the higher. vapor pressure components exert. their.

pumping, action from jet nozzles successively: closer to-thethigh pressure outlet of the-pump. Such. pumps are well. known inthe: art as shown in. Malter U. Sl.Patent 2,112,037; HickmanUl S; Patent 2,206,093 and: Hickman 2,211,329.

Inorder. for. suchpumps' to function mostefiectively, 'itrisnecessary that thevarious. boiler. com-- partments be. isolated except. for a singlexfluid pathway, whichis pref'erably a tortuous pathway, whereby. the pump :fiuidcan:be:fracti0nated during-,travel.. Thus, seepagefromaone boilencomepartment to. another under the. lower ends of. the. chimneys, duetc unevenness: in the bottom ofithe casing 0r slight differences inthe. alignment ofv thelower ends of the chimneys;.,introduces.high vapor pressure. constituents: into. zones. wherein only; lower vapor pressure. constituents. should" be vaporized. This results:v in an: impairment of: the eiiiciency, of. the pump, as regards. both the. ultimate. vacuum attained; a'ndthe pumping speed;

Various expedients. have. been proposedtosolve. the seepage: problem's The chimneys can be welded to the. bottomof: the casing but the resulting pump. cannotzbez disassembled for cleaning or: repairs... Baflies havebeenawelded to the bottom of the pumpcasing intowhich the vapor chim neys-v fit.1 This: is a-costlyv and time consuming operation, however; and 'makes the pumps difiicult. to.- clean... Thexbottom of i the. casing and the ends: of the chimneys have been carefully machined and;the concentricchimneyscareiullyse cured. together. in exact. alignment to insure a. tightfittbetween the. bottomoflv the casing. and the. lower ends ofall oitherchinmeysn Thisis also. a costly expedient, and the. resulting apparatusis subject. to: impairment. by slight warpage of. the. elements.- Grooves-haver been. machinedinto the bottom of the casing to receive the-chimney ends.- Thisis also acostly. pr0cedure,,and pump. fluid tends to char in the grooves which are diificult' toi clean. The. chimneys have-been capped; which effectively prevents seepage but. renders. cleaning. of the ch-imneysmore difficult It. is. accordingly an object ofrthis.-.invention. to provide an improvedvertical fractionatingdifi usion pump.

Another obj ectofi the. invention. is to provide novel. and effectivermeans .for..minimi'zing. seepage of pump fluid in. a verticaldifiusion. pump.

Another object .otthe invention is.tc. provide a simple. diffusion pump. which is readily assembled and disassembled and'. whichhas improved performance characteristics..

Another object of. theinvention is to provide means for improving the. ultimate'vacuum and pumping. speedtof ':aconventionalldifiusion' pump Without necessitating radical; changes instructure.

Other. obiectslwill' ber apparent? from. the descriptionand claims which follow.

These. andTother. objects .are. attained .bymeans. of. this invention a describedmorewfully. hereinafter. with reference. to certain preferred'lembodi ments as illustratedfby. the. drawings.

Of the. drawings Fig. 1 is .a view in: elevation partly broken away. and in section, .ofavertical. diffusion .pump constituting a preferred. embodiment of the. invention; and.

Fig. .2 is-a. partialsection takenlon line-ze-z-of. Fig. l.

With particularsreference toithedrawihgs; the illustrated pump embodying, the: invention com.-- prises: the. combinatiomwith a vertical diffusion. pump of=the-:type including aigenerally cylindricalv pump casing. lit-having. disposed=therein andgenerally concentric;- therewith; vaporzichimneysc .l 1:; I and :i3iwhichraresarranged with; the: lowerlends of; thechimneysrresting.onxthecbottom .l oficasa ing. 10: .to formlconcentric .boiler-rcompartments l5, l6 and. ll, of means;forpreventing seepage-of pump. fluid betweemthe: boiler: compartmentsas described: morecfullwhereinafiter.

Pumplcasing I0 i's provided witn a fiangedhigh' vacuum -i-nlet port l wadapted toflo'e attached to a 5K systemto be evacuated; andafianged higli' presi'.

sure outlet l9 adapted to be connected to a backing pump. A heater element 20 is secured to the bottom Id of casing Ill. The vapor chimneys ll, I2 and i3 terminate upwardly in jet nozzles, one of which is shown in detail at 2|. Chimneys ll, l2 and [3 are rigidly held in spaced-apart relation by spacer brackets 22, 22.

Each chimney i singly notched at its lower end, the notches 23, 23 being spaced so that the notch in one chimney is spaced approximately 180 from the notches in the next adjacent chimneys.

The means for minimizing seepage between the boiler compartments comprises floating collars 24, 25 and 26 cooperating respectively with chimneys H, l2 and I3. Each collar is disposed closely adjacent to and generally concentric with the lower end of one of the chimneys, the collar being sufficiently larger or smaller than the closely adjacent chimney to permit the collar to move vertically relative to the chimney. Preferably the collars are of such diameter as to be out of circumferential contact with the chimneys. Each collar is provided with a single notch in its lower edge as indicated at 21, with the notch 21 preferably being in general alignment with the notch 23 in the closely adjacent chimney to permit passage of pump fluid through the boiler compartments.

The collars 24, 25 and 26 extend upwardly along the chimneys H, 12 and I3 to a height above the normal level of pump fluid in the boiler compartments l5, l6 and I1. Each collar is mounted so that its lower edge rests on the bottom i4of casing Ill, the mounting means being adapted to permit limited vertical displacement of the collar relative to the chimney with which it is associated. In the preferred embodiment shown in the drawings, this is effected by means of a bolt 28 in each chimney extending into an aperture 29 in each collar, the apertures 29, 29 being substantially larger than the bolts 28, 28.

Thus, in the pump embodying the invention, the vapor chimneys are rigidly secured to each other while the collars are loosely mounted on the chimneys for vertical displacement relative to the chimneys. The entire unit of chimneys and collars can be inserted into or removed from the casing as a, unit. The rigid mounting of the chimneys to each other ensures proper spacings in the jet nozzles at all times. The collars, being free to move can drop slightly below the ends of one or more of the chimneys when the bottom of the pump casing is not perfectly flat or when the chimneys are not all of exactly the right length to contact the bottom of the casing.

If, during service, the bottom of the casing becomes slightly warped, the collars automatically adjust for variations in the bottom of the casing.

I have found that the floating collars minimize objectionable seepage of pump fluid under the ends of the chimneys. The necessity for machining the bottom of the casing and the lower ends of the chimneys, or other costly and time-consuming expedients are obviated. The effectiveness of the collars in minimizing seepage is reflected in better performance characteristics as shown by higher ultimate vacuums and increased pumping speeds.

While the invention has been described in considerable detail with reference to a preferred embodiment as shown in the drawings, it will be understood that variations and modifications can be effected within the spirit and scope of being secured together into a unitary chimney assembly, said chimneys being spaced from each other and from said casing and having the lower ends of said chimneys contiguous to the bottom of said casing and forming a plurality of generally concentric boiler compartments, each said chimney having a notch in the lower end of the chimney for permitting flow of pump fluid through said boiler compartments in series, a floating collar disposed around the lower end of each chimney in closely adjacent concentric relation with said chimney, said collars being substantially out of frictional contact with said chimneys and having the lower circumferential edge of each said collar in contact with the bottom of said casing, said collars extending upwardly along said chimneys to a height above the normal level of pump fluid in said boiler compartments, each said collar having a notch in the lower edge thereof in general alignment with the notch in the next adjacent chimney,

' each said collar having a wall opening therein in a localized upper zone of said collar, and pinning means secured to each said chimney and extending into the wall opening in the next adjacent collar, said pinning means being substantially smaller than said Wall opening for permitting limited vertical movement of said collars relative to said chimneys.

2. In a vertical diffusion pump, the combination which comprises a generally cylindrical casing, a bottom for said casing, a plurality of concentric vapor chimneys disposed in said casin and generally concentric with said casing, said chimneys being arranged in spaced relation with each other and with said casing and having the lower ends of said chimneys contiguous to the bottom of said casing and forming a plurality of concentric boiler compartments within said casing, each said chimney having an opening through the wall of said chimney contiguous to the lower end of said chimney and aifording communication between said boiler compartments, a vertically displaceable {floating collar disposed in closely adjacent and generally concentric relation to the lower end of at least one of said chimneys, said collar having an aperture therein in general alignment with the opening in said chimney closely adjacent to said collar, and mounting means securing said collar to said closely adjacent chimney and confining said collar to limited vertical displacement relative to said closely adjacent chimney.

3. In a vertical diffusion pump, the combination comprising a generally cylindrical casing, a bottom for said casing, a plurality of concentric vapor chimneys disposed in said casing and generally concentric with said casing, said chimneys being spaced from each other and from said casing and having the lower ends if said chimneys contiguous to the bottom of said casing and forming a plurality of concentric boiler compartments, each said chimney having an opening through the wall of said chimney contiguous to the lower end of said chimneyfor interconnecting said boiler compartments, a vertically displaceable floating collar for the lower end of each said chimney, each said collar being disposed in closely adjacent and generally concentric relation to the lower end of one of said chimneys, said collars extending upwardly along said chimneys to a height greater than the normal level of pump fluid in said boiler compartments, each said collar having an aperture therein generally coinciding with the opening in the chimney closely adjacent to said collar, means securing said collars to said chimneys, and means asso- 10 Number chimneys.

MERRIAM E. JOHNSON.

References Cited in the file of this patent UNITED STATES PATENTS Name Date 2,291,054 Nelson July 28, 1942 

